Conventionally, as methods for providing a polyester-based fiber with flame retardancy, a method has been known which employs a halogenated cycloalkane compound, such as hexabromocyclododecane, as a flame-retarder component, and which uses a flame-retarder agent obtained by dispersing the flame-retarder component in water by a dispersant.
However, recent increasing concerns over global and living environment protection have led to development of methods for providing a polyester-based fiber with flame retardancy by using as a flame-retarder component a phosphorus-containing compound, which contains no halogen atom, instead of a halogen-containing compound. For example, Japanese Unexamined Patent Application Publication No. 2000-328445 (Document 1) discloses a flame-retardant processing method in which a flame-retarder agent containing resorcinol bis(diphenyl phosphate) emulsified and dispersed in the presence of a surfactant is added to a dyeing liquid and is adsorbed to a polyester-based fiber at the same time of dyeing. Meanwhile, Japanese Unexamined Patent Application Publication No. 2003-193368 (Document 2) discloses a flame-retardant processing method in which: a flame-retarder agent containing an aryl diamino phosphate, such as 1,4-piperazinediyl bis(diaryl phosphate), dispersed in a solvent in the presence of a surfactant is added to a dyeing liquid; the flame-retarder agent is adsorbed to a polyester-based fiber at the same time of dyeing; and the polyester-based fiber is dried and then heat-treated at 170° C. to 220° C. Document 2 also discloses a flame-retardant processing method in which: a polyester-based fiber is dyed; the flame-retarder agent is adhered to polyester-based fiber; and then the polyester-based fiber is dried and heat-treated at 170° C. to 220° C.
However, the flame-retardant processing methods described in Document 1 and Document 2 have difficulty in making the phosphorus flame-retarder component sufficiently absorbed to the polyester-based fiber, which leads to a problem that sufficient flame retardancy cannot be provided to the polyester-based fiber. These methods also have a problem that, owing to ultraviolet light or the like, the phosphamide in the polyester-based fiber causes degradation of the dye in the polyester-based fiber and in turn discoloration thereof.
In addition, phosphate ester-based flame-retarder agents generally have problems such as impacts on fogging properties (haze properties), hydrolytic properties, thermal stability, and dye-affinity; and decrease in light fastness and rubbing fastness. These problems are crucial especially when such flame-retarder agents are used for interior materials for vehicle. For this reason, as a phosphorus flame-retarder agent which can alleviate these problems to a relatively large extent, for example, Japanese Unexamined Patent Application Publication No. 2007-092263 (Document 3) discloses a flame-retarder agent in which triphenylphosphine oxide is used as a flame-retarder component. However, even with the flame-retarder agent disclosed in Document 3, the amount of the triphenylphosphine oxide absorbed into a polyester-based fiber is small, resulting in a problem that sufficient flame retardancy cannot be provided to the polyester-based fiber.